When should/shouldn’t I use forward couplers for injecting crosstalk?

We don’t recommend using forward couplers for injecting crosstalk into serial link systems.

There are no forward couplers in backplane or general serial link systems. Generally, they are wideband systems with channel characteristics unlike PCB t-lines. True power spectral density of the crosstalk is impacted by dielectric, and metal losses in actual PCB transmission systems, and those systems represent models that are used for COM and general serial link analysis. You can’t do any of this with forward couplers.

You should seriously think about using PCB system generated crosstalk, like our XTALK-56 platform. It includes basic crosstalk coupling, via coupling, backplane/connector emulators that include the ability to add crosstalk.

Finally, by having crosstalk structures that have the same loss as our PCB platforms (ISI and XTALK) you can directly determine, easily, how crosstalk impacts transmission reach penalty. By including return loss degradation structures in the XTALK platform you can perform SERDES design of experiments with variables loss, crosstalk, return loss floor through the Nyquist region. Sorry, you can’t do that with forward couplers.

Pluou can add both clock and data to crosstalk in the XTALK platform.

Adding noise to RX input isn’t crosstalk, it is simply noise.

Finally, forward couplers add strange deterministic jitter profiles, while PCB transmission does not. PCB transmission adds DJ exactly like normal transmission PCB.